/Engine/Source/Runtime/GeometryCore/Public/Polygon2.h
Get the vectors from a given vertex to the previous and next Vertices, optionally normalized
void NeighbourVectors ( int VertexIdx, [TVector2](API\Runtime\Core\Math\TVector2)< T > & OutToPrev, [TVector2](API\Runtime\Core\Math\TVector2)< T > & OutToNext, bool bNormalize ) const